The present invention relates to a float actuated shutoff valve operable to shut off the incoming flow of liquid into a closed storage tank when the level of liquid within the tank rises to a predetermined level to prevent overfilling of the tank. Although useful in other applications, the valve of the present application was designed for use in underground fuel storage tanks employed at gasoline service stations.
The standard method of determining the level of fuel in an underground storage tank at a service station is to insert a gauge pole into the tank through the fill pipe. Very few underground tanks are equipped with any sort of measuring device which will give a continuous indication of how much fuel is in the tank, and very few fuel delivery trucks which fill such underground storage tanks are equipped with any indicator which will give a continuous measurement of the amount of fuel discharged from the tank truck. The conventional method of measuring the amount of fuel delivered into the underground storage tank is to utilize the gauge pole before and after, but not during, the fuel delivery. As a result, it is quite common that the underground tank is overfilled and a substantial amount of fuel is spilled when the delivery hose is disconnected from the underground tank fill pipe.
As set forth in the parent applications referred to above, various forms of float actuated shutoff valves have been devised to stop the flow of fuel into the underground tank when the level of fuel within the tank rises to a preselected level, as, for example, 95% of the tank capacity.
Typically, a flapper valve is employed, the valve when open extending vertically upwardly from a horizontal pivot axis at one side of the flow passage, shielded from the downward flow of fuel through the passage. The flapper is pivoted outwardly into the downward flow in response to upward movement of an actuating float by the rising level of fuel within the tank. In such an arrangement, the flapper is driven to its seat with a substantial force generated by the downward flow of fuel, and closure of the flapper valve generates a substantial water hammer which is intended to signal the delivery man that it is time to turn off the valve on the tank truck.
Assuming the delivery man is paying attention and immediately closes the tank truck valve to terminate the flow of fuel into the underground tank, the flapper valve normally is located somewhere below the top of the underground tank fill pipe, and closure of the flapper valve traps a fairly substantial quantity of fuel above the valve in the fill pipe and in the delivery hose downstream of the shutoff valve on the tank truck. The amount of fuel so trapped may be as much as 30-35 gallons, and this fuel will be spilled when the delivery hose is uncoupled from the fill pipe because the closed flapper valve prevents the fuel from draining into the underground tank. Various solutions to this problem have been proposed in the prior art.
A very common solution is to provide a relatively small drain hole through the valve flapper so that when the flapper is closed, fuel trapped above the flapper can drain through the drain hole into the underground tank. While this is a seemingly simple and straightforward solution to the problem outlined above, the sizing of this drain hole is, to some extent, a matter of personal preference. If it could be assumed the delivery man would always be attentive and shut off the tank truck valve immediately upon observing the water hammer effect occasioned by closure of the flapper valve, then the drain hole might be made relatively large in order to provide rapid drainage of the 30-35 gallons trapped above the closed valve. However, if the delivery man does not shut off the tank truck valve fairly promptly after the flapper valve closes, a relatively rapid flow of fuel downwardly through a relatively large drain hole in the closed flapper can result in the overfilling of the tank to the point where the delivery hose cannot be drained.
If, on the other hand, a relatively small diameter drain hole is employed, then a substantial amount of time will be required to drain the delivery hose, and an impatient delivery man may uncouple the delivery hose from the fill pipe before the delivery hose has fully drained.
The parent applications identified above both address this problem utilizing a two stage shutoff valve in which a rise of the level of fuel within the tank to a first level, say 90% of tank capacity, will elevate a first float which closes a first flapper. When closed, the first flapper does not completely close the incoming flow passage but may close, for example, 90% of the passage. In this last example, closure of the first flapper reduces the rate at which fuel flows into the storage tank by 90 % -- in other words, from a normal flow rate of 300-400 gallons per minute to a flow rate of 30-40 gallons per minute. Closure of the first flapper will generate a water hammer effect sufficient to be observable by the delivery man. In the case of a 10,000 gallon storage tank, at the time the first flapper closes, indicating that 9,000 gallons are in the tank, there is still room for another 500 gallons, if filling is to be terminated at 95% capacity, and this affords the delivery man up to 10 or 12 minutes leeway to close the shutoff valve. If the delivery man does not stop fuel delivery before the tank is 95% filled, a second float will actuate a second valve flapper which closes off the remaining portion of the flow passage so that no more fuel can flow into the tank. In this event, fuel will be trapped in the delivery hose.
Where the underground tank fill pipe is provided with an overfill storage container such as that of U.S. Pat. No. 4,793,387, for example, the delivery hose may be simply drained into the overfill container from which it is subsequently drained into the underground tank. Otherwise, drainage of the delivery hose is a time-consuming process since the hose must be drained through the fill pipe and into the underground tank through relatively restricted openings in the overfill valve housing through which valve actuating mechanism coupled to the valve flappers within the housing passes to connect to the actuating floats at the exterior of the valve housing.
The present invention is directed to a two stage valve whose second stage will close at a predetermined maximum level of fuel within the storage tank and will open when the shutoff valve on the tank truck has been closed to permit fuel to drain from the delivery hose into the underground tank, the first stage flapper also being moveable to its open position to accelerate the drainage.